Disk drives are information storage devices that use thin film magnetic media to store data. A typical disk drive includes one or more rotatable disk having concentric data tracks wherein data is read or written. As the disk rotates, a transducer (or "head") is positioned by an actuator to magnetically read data from or write data to the various tracks on the disk.
When a typical contact start/stop (CSS) disk drive is at rest, the head rest upon the surface of the disk. As operation of the drive commences, the disk rotates and the head begins to slide against the surface of the disk. As the disk rotational speed increases, pressure effects caused by air flow between the surface of the disk and an air bearing surface of the head cause the head to float above the disk. Once a predetermined rotational speed and head fly height (i.e. float height) is reached, reading and/or writing of data may commence.
To maximize recording density and to ensure reliable disk operation, disk heads fly in close proximity to the disk surface. To enable low fly heights, a smooth head and a smooth disk surface are preferred. However, close operation of a smooth disk and head can cause "stiction" between the disk and head. Stiction is a type of friction caused by a variety of factors including static and adhesion forces between the disk and head. Stiction between a rotating disk and flying head can cause the head to impact the surface of the disk resulting in data loss and damage to both the disk and head. Stiction also occurs between the disk and head when the disk is at rest. At-rest stiction forces are generally greater than those between a flying head and rotating disk. In some circumstances, the disk rotating motor may not be able to overcome the at-rest stiction forces or the head and disk may incur permanent damage in overcoming these forces. Therefore, to ensure reliable operation of a disk drive, stiction forces must be controlled.
To overcome relatively high levels of at-rest stiction, a disk may include a highly textured landing zone wherein the disk head rest whenever the rotating disk is at rest or below the speed required for head flight. The texture in the landing zone may be increased relative to the remaining disk surface by applying pulsed laser radiation to the landing zone thereby forming regularly spaced bumps. Additionally, for stiction reduction and other reasons, the data storage areas of the surface may also be textured. In general, however, the data surface will still be substantially smooth compared to the landing zone. By including both a highly textured landing zone and a substantially smooth or lightly textured data zone, operational reliability of the disk drive can be improved.
After the data and landing zone are fashioned, the disk may still include undesired aberrations. For example, the disk may include protrusions in the data zone caused by defects in the disk coating process. If such protrusions are greater than the disk head fly height, they can impact the head during drive operation causing a head crash. To reduce this risk, a disk undergoes glide testing before being incorporated in a finished hard disk drive. During glide testing, the disk is placed on a rotating platter and a test head is flown over the surface of the disk. The test head fly height is maintained at or below the expected fly height of an operative drive head. Thus, the glide test system can detect, through sensed collisions, disk aberrations that would affect an operative head. Additionally, by testing the disk at a glide test head height below the nominal operative drive head height, expected deviations in the operative head height can be accounted for.
During glide testing, when the glide head is over the disk's data area, the linear velocity of the disk with respect to the glide head is maintained at a constant value. As a result, the glide test head can be maintained at a constant height. To maintain constant linear velocity, the disk rotation speed is gradually decreased as the glide head moves from smaller to larger radii within the data zone. Conversely, disk rotation speed is gradually increased as the glide head moves from larger to smaller radii in the data zone.
However, when the glide test head transitions from the data zone to the landing zone, the linear velocity of the disk is rapidly increased to obtain a greater landing zone head height compared to the data zone. This requires a step increase in disk speed at the transition point between the landing zone and the data zone. Typically, the glide testing apparatus determines this transition point using predetermined zone radius parameters entered into a glide tester control apparatus. Since the actual transition from the data zone to the landing zone can vary among manufactured disk, the predetermined zone parameters input to the glide tester may not accurately reflect the data and landing zone of the particular disk under test. This reduces the accuracy of the glide test and can reduce the reliability of drives using such tested disk. Consequently, advantages such as improved reliability of a disk drive may be obtained by more accurately determining the transition between a disk's landing zone and data zone during glide testing.